Orthopaedic Component Manufacturing Method and Equipment

ABSTRACT

A system for use in preparing an articulating surface of a component of an orthopaedic implant is provided. The system includes a magnetorheological polishing fluid including a carrier fluid and a plurality of particles suspendable in said carrier fluid. The system also includes a vessel for containing the Magnetorheological polishing fluid. The system also includes a mechanism for delivering the fluid to form a polishing zone and a holder for securing the component and for moveably positioning the articulating surface of the component relative to the polishing zone. The system further includes a controller for determining the rate of material removal from the object, for determining the direction and velocity of movement of the polishing zone relative to the object and for determining the number of cycles of polishing required.

This application is a divisional of co-pending application Ser. No.11/540,167, filed Sep. 29, 2006, which in turn, claims the benefit ofU.S. Provisional Application Ser. No. 60/731,791, filed Oct. 31, 2005,the disclosure of both of the above-identified patent applications areherein totally incorporated by reference in their entirety.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Utility patent application of Provisional patentapplication Attorney Docket No. DEP 5503, U.S. Patent Application No.60/731,791 titled “ORTHOPAEDIC COMPONENT MANUFACTURING METHOD ANDEQUIPMENT” filed Oct. 31, 2005. This application claims priority ofProvisional patent application Attorney Docket No. DEP 5503, U.S. PatentApplication No. 60/731,791 titled “ORTHOPAEDIC COMPONENT MANUFACTURINGMETHOD AND EQUIPMENT” filed Oct. 31, 2005. U.S. Patent Application No.60/731,791 is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of orthopaedics,and more particularly, to an implant for use in arthroplasty.

BACKGROUND OF THE INVENTION

The skeletal system includes many long bones that extend from the humantorso. These long bones include the femur, fibula, tibia, humerus,radius and ulna.

A joint within the human body forms a juncture between two or more bonesor other skeletal parts. The ankle, hip, knee, shoulder, elbow and wristare just a few examples of the multitude of joints found within thebody. As should be apparent from the above list of examples of joints,many of the joints permit relative motion between the bones. Forexample, the motion of sliding, gliding, and hinge or ball and socketmovements may be had by a joint. For example, the ankle permits a hingemovement, the knee allows for a combination of gliding and hingemovements and the shoulder and hip permit movement through a ball andsocket arrangement.

The joints in the body are stressed or can be damaged in a variety ofways. For example, gradual wear and tear is imposed on the jointsthrough the continuous use of a joint over the years. The joints thatpermit motion have cartilage positioned between the bones providinglubrication to the motion and also absorbing some of the forces directto the joint. Over time, the normal use of a joint may wear down thecartilage and bring the moving bones in a direct contact with eachother. In contrast, in normal use, a trauma to a joint, such as thedelivery of a large force, from an accident, for example, an automobileaccident, may cause considerable damage to the bones, the cartilage orto other connective tissue such as tendons or ligaments.

Arthropathy, a term referring to a disease of the joint, is another wayin which a joint may become damaged. Perhaps the best known jointdisease is arthritis, which is generally referred to a disease orinflammation of a joint that results in pain, swelling, stiffness,instability, and often deformity.

There are many different forms of arthritis, with osteoarthritis beingthe most common and resulting from the wear and tear of a cartilagewithin a joint. Another type of arthritis is osteonecrosis, which iscaused by the death of a part of the bone due to loss of blood supply.Other types of arthritis are caused by trauma to the joint while others,such as rheumatoid arthritis, Lupus, and psoriatic arthritis destroycartilage and are associated with the inflammation of the joint lining.

The hip joint is one of the joints that is commonly afflicted witharthropathy. The hip joint is a ball and socket joint that joins thefemur or thighbone with the pelvis. The pelvis has a semisphericalsocket called the acetabulum for receiving a ball socket head in thefemur. Both the head of the femur and the acetabulum are coated withcartilage for allowing the femur to move easily within the pelvis. Otherjoints commonly afflicted with arthropathy include the spine, knee,shoulder, carpals, metacarpals, and phalanges of the hand.

Arthroplasty as opposed to arthropathy commonly refers to the making ofan artificial joint. In severe cases of arthritis or other forms ofarthropathy, such as when pain is overwhelming or when a joint has alimited range of mobility, a partial or total replacement of the jointwithin an artificial joint may be justified. The procedure for replacingthe joint varies, of course, with the particular joint in question, butin general involves replacing a terminal portion of an afflicted bonewith a prosthetic implant and inserting a member to serve as asubstitute for the cartilage.

The prosthetic implant is formed of a rigid material that becomes bondedwith the bone and provides strength and rigidity to the joint and thecartilage substitute members chosen to provide lubrication to the jointand to absorb some of the compressive forces. Suitable materials for theimplant include metals and composite materials such as titanium, cobaltchromium, stainless steel, ceramic and suitable materials for cartilagesubstitutes include polyethylene, ceramics, and metals. A cement mayalso be used to secure the prosthetic implant to the host bone.

A total hip replacement, for example, involves removing the ball shapedhead of the femur and inserting a stem implant into the center of thebone, which is referred to as the medullary canal, or marrow of thebone. The stem implant may be cemented into the medullary canal or mayhave a porous coated surface for allowing the bone to heal directly tothe implant. The stem implant has a neck and a ball shaped head, whichare intended to perform the same functions as a healthy femur's neck anda ball shaped head. The polyethylene cup is inserted into the acetabulumand has a socket for receiving the head on the stem implant.

The polyethylene cup may be positioned directly into the acetabulum.Preferably, the polyethylene cup is secured to a metal member, which isin turn secured to the acetabulum. This metal member is typically calleda cup or a shell. The cup or shell may include a porous coating forpromoting bony in-growth to secure the shell to the acetabulum.Alternatively or in addition the shell may include an opening or aplurality of openings for receiving bone screws to assist in theattachment of the shell to the acetabulum. As an alternative to thepolyethylene cup, a cup of a different material may be inserted into theshell. For example, the cup may be made of a metal, for example, cobaltchromium, stainless steel, or titanium. Alternatively, the cup may bemade of a ceramic.

More recently, the polyethelene cup as a hip cup prosthesis has beenreplaced with a more rigid component. For example, in more recent hipcup prostheses, the cup is made of, for example, a metal or a ceramic.The head may be made of a metal or a ceramic. For example, the cup maybe made of a ceramic and the head may likewise be made of a ceramic.Alternatively, the cup may be made of a metal and the head may likewisebe made of that similar metal. It should be appreciated that a ceramiccup may be utilized with a metal head and a metal cup may be utilizedwith a ceramic head.

To maximize the life of the prosthesis, the accuracy of the dimensionalcharacteristics of the components of the prosthesis as well as thesurface condition, for example the surface finish, is extremely criticalin the life of the prosthesis. Dimensional errors and surface finishimperfections may cause the prosthesis to prematurely wear. Thecomponents that wear on the prosthesis, particularly those that wearrapidly, may lead to reactions with the tissues of the body. Suchreaction to foreign objects is called osteolysis. Osteolysis can damagesoft tissue and further complicate the replacement of the prosthesis.

Attempts have been made to provide for improved finishes and geometriesof the articulating surface of a prosthesis. For example, the surfacesmay be polished by hand by, for example, a rubbing compound or by ametal or cloth buffing wheel. Alternatively, the surfaces may besmoothed by robotic manipulators using similar tools as are used byhand. Alternatively, the components have the articulating surface of theprosthesis may be polished by a finishing device, for example aRotoFinish® tumbling machine. These prior art attempts at providingimproved geometry and finish to the articulating surface of a prostheticcomponent are slow and inaccurate. Further, the use of the continualattempts to improve the finish on the part may affect its geometry orshape. Imperfections in shape and or finish may greatly reduce theoperating life of the prosthesis and may lead to osteolysis.

The present invention is adapted to solve at least some of theaforementioned problems with the prior art.

SUMMARY OF THE INVENTION

This invention is directed to improved devices and methods for polishingorthopaedic implant components in a Magnetorheological Polishing fluid(hereinafter referred to as “MP-fluid”). More particularly, thisinvention is directed to a highly accurate method of polishing implantcomponents in a MP-fluid that may be automatically controlled and mayimprove polishing devices.

These fluids are of at least two types. The first type of fluids aremixtures of abrasive particles and magnetic particles. The abrasiveparticles are in suspension and magnetic particles are in suspension ina fluid. The magnetic particles are coated with Teflon®, a trademark ofE.I. DuPont de Nemours and Company, to protect them from degradation.These particles could be suspended in solutions of glycerin, glycol,water, oil, alcohol, or mixtures thereof. When a magnetic field isapplied, the magnetic particles create a plastic zone, and the abrasiveparticle provide for polishing action.

The first type of fluids are used in manufacturing equipment thatutilizes the MP-fluid finishing process is commercially available fromQED Technology, Inc., Rochester, N.Y. and sold as the Q-22MRF System.

The second type of fluid includes a finer sized particle having acombination of magnetic and abrasive properties. The particles are, forexample iron (Fe) metal nanoparticles that are coated with SiC. Theparticles may, alternatively, be, for example, cobalt (Co), samarium(Sm), neodymium (Nd), erbium (Eb), copper (Cu), nickel (Ni), or silver(Ag). The particles should be magnetic. Silicon carbide (SiC) is a hardfunctional material and has good thermal conductivity. Coating the metalnanopowder with SiC can prevent oxidation of the metal nanopowder andimprove the dispersion and mechanical property of the nanopowder. Theseparticles also could be suspended in solutions of glycerin, glycol,water, oil, alcohol, or mixtures thereof.

A research group headed by Joseph Lik Hang Chau at the Ultrafine PowdersLaboratory, Materials Research Laboratories, Industrial TechnologyResearch Institute, Taiwan, has tested such second type of particles. ALexis Nexis article entitled “MICROWAVE PLASMA SYNTHESIS OF ENCAPSULATEDMETAL NANOPOWDERS” available on the Lexis Nexis website furtherdescribes the activities of Mr. Chau and is hereby incorporated hereinin its entities by reference.

When mentioning MP fluids herein it will be understood to mean thealternative use of either the type one fluids or the type two fluidsmentioned above.

The method of this invention comprises the steps of creating a polishingzone within a MP-fluid; bringing an implant component to be polishedinto contact with the polishing zone of the fluid; determining the rateof removal of material from the surface of the object to be polished;calculating the operating parameters, such as magnetic field intensity,dwell time, and spindle velocity for optimal polishing efficiency; andmoving at least one of said object and said fluid with respect to theother according to the operating parameters.

The polishing device includes an object to be polished; and a MP-fluid,which may or may not be contained within a vessel. The device alsoincludes means for inducing a magnetic field, and mean for moving one ormore of these components with respect to one or more of the othercomponents. The orthopaedic component or object to be polished isbrought into contact with the MP-fluid, and the MP-fluid, the means forinducing a magnetic field, and/or the object to be polished are put intomotion, thereby allowing all facets of the object to be exposed to theMP-fluid.

In the method and devices of this invention, the MP-fluid is acted uponby a magnetic field in the region where the fluid contacts the object tobe polished. The magnetic field causes the MP-fluid to acquire thecharacteristics of a plasticized solid whose yield point depends on themagnetic field intensity and the viscosity. The yield point of the fluidis high enough that it forms an effective polishing surface, yet stillpermits movement of abrasive particles. The effective viscosity andelasticity of the MP-fluid when acted upon by the magnetic fieldprovides resistance to the abrasive particles such that the particleshave sufficient force to abrade the work piece.

This invention is directed to improve devices and methods for polishingorthopaedic articulating surfaces MP-fluid. More particularly, thisinvention is directed to a highly accurate method of polishing thearticulating surfaces of orthopaedic joint implant components in aMP-fluid, which, may be automatically controlled, and to improvepolishing devices.

The method of this invention includes the steps creating the polishingzone within a MP-fluid, bringing objects into contact with the polishingzone of the fluid, determining the rate of removal of material from thesurface of the object to be polished, controlling the operatingparameters, such as magnetic field intensity, cycle time and spindlevelocity for polishing efficiency, and translating at least one of theobject and the fluid with respect to each other according to theoperating parameters.

The polishing device includes an orthopaedic component or object to bepolished, a MP-fluid, which may or may not be contained within a vessel,means for inducing a magnetic field, and means for moving at least oneof these components in respect to the other or more of the othercomponents. The object to be polished is brought into contact with theMP-fluid and the unique MP-fluid together with means for inducing amagnetic field, and/or the object to be polished are put into motion,thereby allowing all facets of the object to be exposed to the MP-fluid.

In the method and devices for this invention, the MP-fluid is reactedupon by a magnetic field in the region where the fluid contacts theobject to be polished. The magnetic field causes the MP-fluid to acquirethe characteristics of a plasticized solid whose yield point depends onthe magnetic field intensity and the viscosity. The yield point of thefluid is high enough that it forms an effective polishing surface, yetstill permits movement of abrasive particles. The effective viscosityand elasticity of the MP-fluid when acted upon by the magnetic field,provides assistance to the abrasive particles such that the particleshave sufficient force to abrade the work piece.

The process of the present invention is best understood by thinking ofthe MP-fluid as a compliant replacement for a conventional sub-aperturepolishing lap. The fluid's viscosity is magnetically manipulated whilein contact with the working surface to create a sub-aperture polishinglap that conforms to the surface. The process of the current inventionhas distinctive values that eliminate the problems of classicalpolishing.

The fluid characterizes and operates the polishing tool. The polishingtool adapts to complex shapes because of this compliant fluid. Theprocess removal rates are very high resulting in short process times.

A small quantity of MP-fluid is loaded into the vessel, for example, aclosed-loop fluid delivery system wherein fluid properties such as, forexample, temperature and viscosity, are continually monitored andcontrolled. The fluid is drawn out of the conditioner and extruded ontoa, for example, rotating spherical wheel, in a thin ribbon that willcontact the articulating surface of the prostheses. The ribbon is thenmoved via suction and fed back into the conditioner.

An electromagnet, located, for example, below the, polishing wheel, hasspecifically designed pole pieces that extend up to the underside of theapex of the wheel rim. The pole pieces exert a strong local magneticfield gradient over the upper side of the wheel. When the MP-fluidpasses through the magnetic field, it stiffens in milliseconds, and thenreturns to its original fluid state as it leaves the field again inmilliseconds.

This precisely controlled zone of magnetized fluid becomes the polishingtool when an articulating surface is placed into the fluid in the zone.The stiffened fluid ribbon is squeezed from its original thickness ofabout two (2) millimeters to about one (1) millimeter. The squeezingresults in significant sheer stress at subsequent polishing pressureover that section of the articulating surface of the orthopaedicimplant. At the same instance the MP-fluid conforms to the localcurvature of the articulating surface being polished.

Manufacturing equipment that utilizes the MP-fluid finishing process iscommercially available from QED Technology, Inc., Rochester, N.Y. andsold as the Q-22MRF System. The use of such equipment to polish surfacesis more fully described in U.S. Pat. No. 5,449,313 and U.S. Pat. No.5,577,948 assigned to Byelocorp Scientific Inc., Rochester, N.Y., andhereby incorporated by reference in its entireties.

According to an aspect of the present invention, a system for use inpreparing an articulating surface of a component of an orthopaedicimplant is provided. The system includes a magnetorheological polishingfluid including a carrier fluid and a plurality of particles suspendablein said carrier fluid. The system also includes a vessel for containingthe magnetorheological polishing fluid. The system also includes amechanism for delivering the fluid to form a polishing zone and a holderfor securing the component and for moveably positioning the articulatingsurface of the component relative to the polishing zone. The systemfurther includes a controller for determining the rate of materialremoval from the object, for determining the direction and velocity ofmovement of the polishing zone relative to the object and fordetermining the number of cycles of polishing required.

These fluids are of at least two types. The first type of fluids aremixtures of abrasive particles and magnetic particles. The abrasiveparticles are in suspension and magnetic particles are in suspension ina fluid. The magnetic particles are coated with Teflon®. These particlescould be suspended in solutions of glycerin, glycol, water, oil,alcohol, or mixtures thereof. When a magnetic field is applied, themagnetic particles create a plastic zone, and the abrasive particleprovide for polishing action. The second type of fluid includes a finersized particle having a combination of magnetic and abrasive properties.The particles are, for example iron (Fe) metal nanoparticles that arecoated with SiC. These particles also could be suspended in solutions ofglycerin, glycol, water, oil, alcohol, or mixtures thereof.

In another aspect, the present invention provides a method of preparinga component of a prosthetic implant for use in orthopaedic surgery. Themethod includes the steps of creating a polishing zone within aMagnetorheological polishing fluid and controlling the consistency ofthe fluid in the polishing zone. The method includes the steps ofbringing the object into contact with the polishing zone of the fluidand causing the object and the polishing zone to move with respect toeach other. The method further includes the steps of determining therate of material removal for the object and determining the directionand velocity of movement of the polishing zone relative to the object.The method includes the step of determining the number of cycles ofpolishing required.

In another aspect of this method, the step of determining the rate ofmaterial removal for the object includes determining the spatialdistribution of material removal.

In another aspect of this method, the movement of the polishing zonerelative to the object is continuous.

In another aspect of this method, the step of determining the directionand velocity of movement of the polishing zone relative to the objectincludes determining the size of a contact section of the object incontact with the polishing zone at any given time, determining thethickness of the material layer to be removed during one cycle ofpolishing, and determining the velocity of the polishing zone.

In another aspect of this method, the movement of the polishing zonerelative to the object is in discrete steps.

In another aspect of this method, the step of determining the directionand velocity of movement of the polishing zone relative to the objectinclude determining the size of a contact section of the object incontact with the polishing zone at any given time, determining thedisplacement of the polishing zone in a single step, determining thecoefficient of overlapping, determining the thickness of the materiallayer to be removed during one cycle of polishing, determining the dwelltime for each step of polishing, and determining the number of stepsrequired.

In another aspect of this method, the steps further include displacingthe object from its vertical axis to an angle.

In another aspect of this method, the object is displaced from itsvertical axis to an angle at a continuous velocity.

In another aspect of this method, the step of displacing the object fromits vertical axis to an angle at a continuous velocity further includesdetermining the angle dimension of the contact spot, determining thethickness of the material layer to be removed during one cycle ofpolishing, and determining the angular velocity of the displacement ofthe object to an angle.

In another aspect of this method, the object is displaced from itsvertical axis to an angle in discrete steps.

In another aspect of this method, the step of displacing the object fromits vertical axis to an angle in discrete steps further includesdetermining the angle dimension of the contact spot, determining thethickness of the material layer to be removed during one cycle ofpolishing, determining the value of the angle displacement of a singlestep, determining the coefficient of-overlapping, and determining thedwell time at each step.

In another aspect of this method, the magnetorheological polishing fluidincludes magnetic particles coated with abrasive particles.

In another aspect of this method, the step of controlling the propertiesof the magnetorheological polishing fluid includes replenishing thecarrying fluid during polishing.

In another aspect of this method, the magnetorheological polishing fluidincludes a combination of abrasive particles and magnetic particles.

In another aspect of this method, the magnetorheological polishing fluidis contained within a vessel having a reference surface.

In another aspect of this method, the vessel is moved relative to theobject.

In another aspect of this method, the vessel is rotated at specifiedvelocities.

In another aspect of this method, the polishing zone is nominally onethird of the surface area of the object or less.

In another aspect of this method, the step of creating a polishing zonewithin a magnetorheological polishing fluid includes the steps ofinducing a magnetic field in the vicinity of the magnetorheologicalpolishing fluid, and controlling the direction and intensity of themagnetic field.

In another aspect of this method, the step of controlling the polishingof the object is accomplished by controlling the magnetic fieldintensity and the location of the polishing zone relative to the surfaceof the object.

In another aspect of this method, the step of polishing is controlled bya programmable control unit.

In another aspect of this method, the magnetic field is created by ameans for inducing a magnetic field which is located outside of thevessel.

In another aspect of this method, the step of creating a polishing zonewithin a magnetorheological polishing fluid includes subjecting theMagnetorheological polishing fluid to a non-uniform magnetic field,having magnetic field lines that are perpendicular to the gradient ofsaid field, in a region adjacent to the object.

In another aspect of this method, the gradient of the magnetic field isdirected toward the bottom of the vessel reference surface.

In another aspect of this method, the method further includes the stepof determining the clearance between the object and the vessel referencesurface.

In another aspect of this method, the magnetorheological polishing fluidis used to polish abrasive material therein.

In another aspect, the present invention provides a machine forpreparing a surface of a component of a prosthetic implant for use inorthopaedic surgery. The machine includes a magnetorheological polishingfluid including a carrier fluid and a plurality of particles suspendablein the carrier fluid. The machine also includes a frame and a vessel forstoring the Magnetorheological polishing fluid. The vessel isoperatively connected to the frame. The machine also includes a meansfor subjecting the Magnetorheological polishing fluid to the surface ofthe component. The means for subjecting the Magnetorheological polishingfluid to the surface of the component is operatively connected to theframe. The machine further includes a means for creating relative motionbetween the Magnetorheological polishing fluid and the surface of thecomponent. The means for creating relative motion is operativelyconnected to the frame.

In another aspect of the machine of the present invention, the vessel isadapted for receiving the component and for submersing at least aportion of said component in magnetorheological polishing fluid.

In another aspect of the machine of the present invention, the devicefor subjecting the magnetorheological polishing fluid to the surface ofthe component includes a pump operatively connected to the vessel forapplying the magnetorheological polishing fluid to the surface of thecomponent.

In another aspect of the machine of the present invention, the devicefor creating relative motion between the magnetorheological polishingfluid and the surface of the component includes rotating the componentrelative to the magnetorheological polishing fluid.

In another aspect of the machine of the present invention, the devicefor creating relative motion between the magnetorheological polishingfluid and the surface of the component includes means for flowing themagnetorheological polishing fluid on the surface of the component.

In another aspect of the machine of the present invention, the means forflowing the magnetorheological polishing fluid on the surface of thecomponent includes a pump.

In another aspect of the machine of the present invention, the machinefurther includes a surface finish-measuring device. The surface finishmeasuring device is operatively connected to the frame for providing ameasurement of the surface finish of the articulating surface of thecomponent.

In another aspect of the machine of the present invention, the surfacefinish measuring device uses optics to measure the surface finish of thearticulating surface of the component.

In another aspect of the machine of the present invention, the surfacefinish measuring device uses electrical conductivity to measure thesurface finish of the articulating surface of the metal component.

In another aspect of the machine of the present invention, the machinefurther includes a magnetic field generating device. The magnetic fieldgenerating device is operatively connected to the frame for exposing thearticulating surface of the metal component to a magnetic field to alterthe metal removing characteristics of the machine.

In another aspect of the machine of the present invention, the magneticfield generating device provides an adjustable magnetic field.

In another aspect of the machine of the present invention, the machinefurther includes a heater operatively connected to the frame. The heaterfor elevating the temperature of the articulating surface of thecomponent to alter the material removing characteristics of the system.

In another aspect of the machine of the present invention, the machinefurther includes a particle measuring device operatively connected tothe frame. The particle measuring device measures the content ofparticles in the magnetorheological polishing fluid.

In another aspect of the machine of the present invention, the particlemeasuring device includes a light emitting device for emitting lightonto the magnetorheological polishing fluid.

In another aspect of the machine of the present invention, the particlemeasuring device further includes a meter for measuring the lightreflected from the magnetorheological polishing fluid.

In another aspect of the machine of the present invention, the particlemeasuring device measures at least one of the turbidity, the absorptionand the reflectance of the magnetorheological polishing fluid.

In another aspect of the machine of the present invention, the particlemeasuring device measures the electrical conductivity of themagnetorheological polishing fluid.

In another aspect of the machine of the present invention, themagnetorheological polishing fluid includes magnetic particles coatedwith abrasive particles.

In another aspect of the machine of the present invention, theMagnetorheological polishing fluid includes a combination of abrasiveparticles and magnetic particles.

In another aspect of the machine of the present invention, the surfacefinish measuring device uses interferometry to measure the surfacefinish of the articulating surface of the component.

In yet another aspect of the present invention a method of preparing acomponent of a prosthetic implant for use in orthopaedic surgery isprovided. The method includes the steps of, creating a polishing zonewithin a Magnetorheological polishing fluid, controlling the consistencyof the fluid in the polishing zone, bringing the object into contactwith the polishing zone of the fluids, and causing the object and thepolishing zone to move with respect to each other.

In another aspect, the present invention provides a fixture for securingan orthopaedic implant to a machine while applying a Magnetorheologicalpolishing fluid to the articulating surface of the implant. The fixtureincludes a body, means to secure the body to the machine, and means tosecure the implant to the body.

The technical advantages of the present invention include the ability toprovide quicker polishing time and less labor in providing surfacefinishes to the articulating surface of orthopaedic prosthesis. Forexample, according to one aspect of the present invention, a process isprovided to polish the articulating surface of an orthopaedic implantwith a MP-fluid. The fluid is acted upon by a magnetic field in theregion where the fluid contacts the object to be polished. The fieldcauses the fluid to acquire characteristics of a plasticized solid whoseyield point depends on the field intensity and the viscosity. The yieldpoint of the fluid is high enough that the fluid forms an effectivepolishing surface while still permitting movement of abrasive particles.Thus, the present invention provides for quicker polish times and lesslabor to polish an articulating surface of an orthopaedic implant.

The technical advantages of the present invention include the ability tolower surface finishes while improving geometrical dimensions on thearticulating surface of an orthopaedic implant. For example, accordingto another aspect of the present invention, a machine is provided thatutilizes a MP-fluid that is acted upon by a magnetic field in the regionwhere the fluid contacts the object to be polished. The field causes thefluid to acquire the characteristics of a plasticized solid. The yieldpoint of the fluid is high enough to permit effective polishing of thesurfaces. The work piece is held and the polishing intensity isdistributed along the articulating surfaces of the prosthesis such thatthe surface finish may be improved while also potentially improving thegeometry of the articulating surface. Thus, the present inventionprovides for improved accuracy of the dimensioning of the articulatingsurface of the orthopaedic implant.

The technical advantages of the present invention include the ability tolower surface finish while improving geometrical dimensions on thearticulating surface of an orthopaedic implant. For example, accordingto another aspect of the present invention, a machine is provided thatutilizes a MP-fluid that is acted upon by a magnetic field in the regionwhere the fluid contacts the object to be polished. The field causes thefluid to acquire the characteristics of a plasticized solid. The yieldpoint of the fluid is high enough to permit effective polishing of thesurfaces. The work piece is held and the polishing intensity isdistributed along the articulating surfaces of the prosthesis such thatthe geometry of the articulating surface is improved while also loweringthe surface finish. The improved form or geometry may be achieved bytaking measurements of the implant, i.e. interferometric data, andfeeding this information into the controller so that the magnetic fieldis applied only to the “high” spots that need reduction to achieveperfect form. Thus, the present invention provides for improved accuracyof the dimensioning of the articulating surface of the orthopaedicimplant.

The technical advantages of the present invention further include theability to reduce orthopaedic implant wear, lengthen orthopaedic implantlife, and lessen the incidence and effects of osteolysis. For example,according to another aspect of the present invention, a method isprovided for improving the surface finish of the articulating surface ofan orthopaedic implant such that the wear to the articulating surface ofthe implant is reduced, thus lengthening implant life and reducingosteolysis occurrence. The MP-fluid is acted upon by a magnetic field inthe region where the fluid contacts the object to be polished. Theeffective viscosity and elasticity of the fluid when acting upon theorthopaedic component provides resistance to abrasive particles such asa particle to abrade the work piece. Thus the present invention providesfor improved surface finish and a longer orthopaedic implant life.

The technical advantages of the present invention include the ability toprovide longer life and less wear on the orthopaedic implant. Forexample, according to another aspect of the present invention, a methodis provided for polishing an orthopaedic implant-articulating surface.The process includes the steps of presenting the orthopaedic implantarticulating surface to a flow of MP-fluid which acts upon the surfaceand provides resistance to the abrasive particles such that theparticles have sufficient force to abrade the work piece and smooth thesurfaces. Thus the present invention provides for longer life and lesswear on the orthopaedic implant-articulating surface.

Other technical advantages of the present invention will be readilyapparent to one skilled in the art from the following figures,descriptions and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic drawing of a polishing device for use with anembodiment of the present invention;

FIG. 1A is a schematic drawing of another polishing device for use withanother embodiment of the present invention;

FIG. 1B is a schematic drawing of another polishing device for use withanother embodiment of the present invention;

FIG. 1C is a schematic drawing of another polishing device for use withanother embodiment of the present invention;

FIG. 1D is a schematic drawing of another polishing device for use withanother embodiment of the present invention;

FIG. 1E is a schematic drawing of another polishing device for use withanother embodiment of the present invention;

FIG. 1F is a schematic drawing of another polishing device for use withanother embodiment of the present invention;

FIG. 2 is a schematic view, partially in cross-section, of anotherpolishing device for use with another embodiment of the presentinvention for flat work pieces;

FIG. 3 is a schematic view, partially in cross-section, of anotherpolishing device for use with another embodiment of the presentinvention for use with convex work pieces;

FIG. 4 is an enlarged view of a portion of the apparatus of FIG. 3;

FIG. 5 is a cross-sectional side view of a polishing device for use withan embodiment of the present invention;

FIG. 6 is a cross-sectional side view of a polishing device for use withanother embodiment of the invention;

FIG. 7 is a perspective view of a polishing machining that may beutilized in performing the present invention;

FIG. 8 is a partial perspective view of the polishing machining of FIG.7;

FIG. 9 is an enlarged partial perspective view of the polishingmachining of FIG. 7;

FIG. 10 is a plan view of a hip stem for use with the polishing deviceof an embodiment of the present invention;

FIG. 11 is a plan view of the hip stem of FIG. 10 implanted in a femur;

FIG. 12 is a partial plan view partially in cross-section of a polishingdevice for cooperation with an internal periphery of a hip cup inaccordance with an embodiment of the present invention;

FIG. 12A is a partial plan view partially in cross-section of apolishing device for cooperation with an internal periphery of a hip cupsimilar to that of FIG. 12 except that the slits are vertical ratherthan horizontal in accordance to another embodiment of the presentinvention;

FIG. 13 is a partial plan view partially in cross-section of lappingwheel for cooperation with a recessed face of a knee tibial tray inaccordance with another embodiment of the present invention;

FIG. 13A is a partial plan view partially in cross-section of anotherlapping wheel for cooperation with a recessed face of a knee tibial trayin accordance with yet another embodiment of the present invention;

FIG. 13B is a partial plan view partially in cross-section of yetanother lapping wheel for cooperation with a recessed face of a kneetibial tray in accordance with a further embodiment of the presentinvention;

FIG. 14 is a partial plan view partially in cross-section of lappingtool for cooperation with a recessed face of a knee tibial tray inaccordance with another embodiment of the present invention;

FIG. 15 is a top view of a knee tibial tray for use in performingorthopaedic surgery that may be machined in accordance with yet anotherembodiment of the present invention;

FIG. 16 is a top view of another knee tibial tray for use in performingorthopaedic surgery that may be machined in accordance with yet anotherembodiment of the present invention;

FIG. 17 is a plan view of the knee tibial tray of FIG. 16;

FIG. 17A is a schematic drawing of a polishing device for cooperationwith the bearing surface of the knee tibial tray of FIG. 17;

FIG. 18 is a partial plan view partially in cross-section of a vertebralorthopaedic implant for use in performing spine orthopaedic surgery thatmay be machined in accordance with yet another embodiment of the presentinvention;

FIG. 18A is a partial plan view partially in cross-section of aCharite'® vertebral orthopaedic implant for use in performing spineorthopaedic surgery that may be machined in accordance with a furtherembodiment of the present invention;

FIG. 18B is a schematic drawing of a polishing device for cooperationwith the convex periphery of the outer components of the vertebralorthopaedic implant of FIG. 18 or with the convex periphery of the innercomponent of the Charite'® implant of FIG. 18A;

FIG. 18C is a schematic drawing of a polishing device for cooperationwith the concave periphery of the central component of the implant ofFIG. 18 or with the concave periphery of the outer components of theCharite'® implant of FIG. 18A;

FIG. 19 is a partial plan view partially in cross-section of a kneefemoral implant for use in performing knee orthopaedic surgery that maybe machined in accordance with yet another embodiment of the presentinvention;

FIG. 19A is a schematic drawing of a polishing device for cooperationwith the articulating arcuate periphery of the implant of FIG. 19;

FIG. 20 is a partial plan view partially in cross-section of a glenoidimplant for use in performing shoulder orthopaedic surgery that may bemachined in accordance with yet another embodiment of the presentinvention;

FIG. 20A is a schematic drawing of a polishing device for cooperationwith the concave periphery of the implant of FIG. 20;

FIG. 21 is a partial plan view partially in cross-section of a kneetibial implant for use in performing knee orthopaedic surgery that maybe machined in accordance with yet another embodiment of the presentinvention;

FIG. 21A is a schematic drawing of a polishing device for cooperationwith the articulating periphery of the implant of FIG. 21;

FIG. 22 is a plan view of a humeral implant for use in performingshoulder orthopaedic surgery that may be machined in accordance with yetanother embodiment of the present invention;

FIG. 22A is a schematic drawing of a polishing device for cooperationwith the articulating hemispherical periphery of the implant of FIG. 22;

FIG. 23 is a process flow diagram of a method of preparing anarticulating surface of a prosthetic component for use in jointarthroplasty surgery in accordance with yet another embodiment of thepresent; and

FIG. 24 is a process flow diagram for a yet another method of preparingan articulating surface of a prosthetic component for use in jointarthroplasty surgery according to a further embodiment of the presentinvention.

Corresponding reference characters indicate corresponding partsthroughout the several views. Like reference characters tend to indicatelike parts throughout the several views.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention and the advantages thereof are bestunderstood by referring to the following descriptions and drawings,wherein like numerals are used for like and corresponding parts of thedrawings.

According to the present invention and referring to FIG. 1, anembodiment of the present invention is shown as system 10. System 10 isutilized for preparing an articulating surface 2 of a component 4 of anorthopaedic implant 6. The articulating surface 2 may, as shown in FIG.1, be a convex surface, for example a portion of the component 4. Thecomponent 4, as shown in FIG. 10, may be in the form of an orthopaedichip implant head. The orthopaedic implant 6 may, as shown in FIG. 1, bein the form of a hip prosthesis. It should be appreciated that theorthopaedic implant 6 may, alternatively, be any orthopaedic jointcomponent. Components with flat or convex peripheries, such as kneefemoral components, hip heads, hip stem components, tibial trays, andhumeral heads are particularly well suited for use with the system 10.

The system 10, as shown in FIG. 1, includes a vessel 12 for containing afluid 14. The vessel 12 may be any vessel capable of containing a fluid,for example fluid 14. The vessel 12 may, as shown in FIG. 1, be usedstrictly as a reservoir to maintain and contain a portion of the fluid14 or may, as shown later, be utilized to submerse a portion of theimplant or work piece for polishing.

The fluid 14 may, as shown in FIG. 1, include a magnetic particle 16,which is suspendable in the fluid 14 to form a MP-fluid 18.

Composition of the MP-fluid 18 may be any fluid capable of performingwithin the aspects of the present invention. The MP-fluid is preferablyas described in U.S. Pat. No. 5,449,313 incorporated herein in itsentirety by reference. U.S. Pat. No. 5,577,948 is also incorporated inits entirety herein by reference.

MP fluids 18 are of at least two types. The first type of fluids ismixtures of abrasive particles and magnetic particles. The abrasiveparticles are in suspension and magnetic particles are in suspension ina fluid. The magnetic particles are coated with Teflon®, a trademark ofE.I. DuPont de Nemours and Company, to protect them from degradation.These particles could be suspended in solutions of glycerin, glycol,water, oil, alcohol, or mixtures thereof. When a magnetic field isapplied, the magnetic particles create a plastic zone, and the abrasiveparticles provide for polishing action.

The first type of fluids are used in manufacturing equipment thatutilizes the MP-fluid finishing process is commercially available fromQED Technology, Inc., Rochester, N.Y. and sold as the Q-22MRF System.

In an embodiment of the present invention, the fluid comprises aplurality of magnetic particles, a stabilizer, and a carrying fluidselected from the group consisting of water and glycerine. In anotherembodiment, the magnetic particles 16, (preferably carbonyl ironparticles), are coated with a protective layer of a polymer materialwhich inhibits their oxidation. The protective layer is preferablyresistant to mechanical stress as much as is practical. In anotherpreferred embodiment, using the coating materialpolytetrafluoroethylene, PTFE, (commonly known as Teflon®), theparticles may be coated by the usual process of micro-capsulization.

Heretofore, the utilization of machines embodying the MP-fluid polishingprocess have been limited to its use to polish glass and plasticmaterials. Thus, it should be appreciated that the selection of theMP-fluid previously selected to polish such plastic, glass and ceramicmaterials may not be as effective for polishing metals. Further, itshould be appreciated that the magnetic and thermal conductivity ofmetals utilized in orthopaedic implants may be quite different than thatof the ceramics and glass previously used as the work piece in suchequipment.

Due to the oxidizing nature of metals, the polishing media should beselected such that the acidity or pH of the polishing media not bechemically reactive with the metal of the articulating component of theorthopaedic implant to be polished. The pH of the polishing media shouldbe adjusted to more favorably effect the polishing of metals. Forexample, the pH of the polishing media should be about 6.2 to 7.8 PH.Preferably, the polishing media will be from about 6.8 to 7.2.Appropriate acidic and basic materials may be added to the polishingmedia to obtain a desired PH for the polishing media.

To accommodate the polishing of the articulating surface of the metalorthopaedic implant, the RE-DOX or oxidation-reduction potential of thepolishing media should be adjusted to more favorably effect thepolishing of metals. Material may be added to the MP-fluid that willadjust the oxidation-reduction potential of the polishing media. Forexample, material that will affect the ability of electrons to flowwithin the polishing media should be adjusted to provide for a polishingmedia that more favorably effects the polishing of the metals.

When selecting the optimal material for the MP-fluid 18 for the system10, the particles may be selected to provide for Nano-sized particles.That is, those particles that have a size of less than 50 nanometers forthe abrasive media. Such smaller sized nano-particles may provide betterfinishes for metal substrates. Such nano-sized particles are readilyavailable and can be obtained by proper processing of commerciallyavailable particles.

The MP-fluid 18 for the system 10 may be in the form of carbo-nitrideparticles. Such carbo-nitride particles may be utilized as the abrasivemedia within the MP-fluid 18. Such carbo-nitride particles may providefor quicker and better finishing of metal surfaces.

As an alternative, the MP-fluid 18 of the system 10 for use to polisharticulating surfaces of metallic orthopaedic implants may be in theform of a bonded abrasive magnetic particle system. Such a bondedabrasive magnetic particle system may be in the form of an aluminumoxide, which may be bonded to ferrous oxide using polyfunctional silanemolecules, such as trimethoxysilane. Such a bonded abrasive magneticparticle system may provide for improved polishing of metallic surfaceswith a MP-fluid.

The second type of fluid includes a finer sized particle having acombination of magnetic and abrasive properties. The particles are, forexample iron (Fe) metal nanoparticles that are coated with SiC. Theparticles may, alternatively, be cobalt (Co), samarium (Sm), neodymium(Nd), erbium (Eb), copper (Cu), nickel (Ni), or silver (Ag). Theparticles should be magnetic. Silicon carbide (SiC) is a hard functionalmaterial and has good thermal conductivity. Coating the metal nanopowderwith SiC can prevent oxidation of the metal nanopowder and improve thedispersion and mechanical property of the nanopowder. These particlesalso could be suspended in solutions of glycerin, glycol, water, oil,alcohol, or mixtures thereof.

The second type of fluid provides for a finer sized particle having acombination of magnetic and abrasive properties, and is expected toprovide better finishing results for medical implants without the needfor a 2-part MP-fluid. For example one could achieve better uniformity,have a simpler system, and provide a better finish.

A research group headed by Joseph Lik Hang Chau at the Ultrafine PowdersLaboratory, Materials Research Laboratories, Industrial TechnologyResearch Institute, Taiwan, has tested such second type of particles. ALexis Nexis article entitled “MICROWAVE PLASMA SYNTHESIS OF ENCAPSULATEDMETAL NANOPOWDERS” available on the Lexis Nexis website furtherdescribes the activities of Mr. Chau and is hereby incorporated hereinin its entities by reference.

Magnetic nanoparticles are conventionally prepared be techniques such assolution-phase chemical reduction, thermal decomposition, mechanicalattrition. Recently, techniques such as gas-condensation and microwaveplasma synthesis have been used. Magnetic nanoparticles owing to theirincreased surface area have a great affinity to readily react withoxygen, which can result in changes of physical and chemical propertiesof the nanoparticles. Therefore, encapsulation of these nanoparticles isnecessary to prevent further growth, oxidation, and particleagglomeration to retain its original properties. Already, attempts tomake this encapsulation have been carried out by polymer stabilizationof nanoparticles, silica coatings on metal nanoparticles (iron, copper,nickel).

Silicon carbide (SiC) is a hard functional material and has good thermalconductivity. Coating the metal nanopowder with SiC can preventoxidation of the metal nanopowder and improve the dispersion andmechanical property of the nanopowder. A research group headed by JosephLik Hang Chau at the Ultrafine Powders Laboratory, Materials ResearchLaboratories, Industrial Technology Research Institute, Taiwan, hasdeveloped a two-stage microwave plasma synthesis process to producecobalt (Co) metal nanoparticles and to finally coat them with SiC. Thetechnique developed is a two-step microwave plasma synthesis process.The first step involves preparing pure metal nanoparticles. The averagesize of the core metal nanoparticles can be controlled in the firststage of the synthesis before the coating of the second layer. The SiCis then coated during the second stage immediately after thesynthesizing of the pure metal nanopowder.

The microwave plasma unit consisted of a microwave source, resonancechamber, reactor chamber with a quartz tube inside, heat exchanger, anda powder collector. The synthesis was carried out in the reaction regionpassing a single cavity mode of 2.45 GHz microwave system. Cobalt (II)chloride (CoCl2) was used as the precursor (feed rate of 0.74 g/min) forCo nanopowder synthesis. Whereas, silicon tetrachloride (SiCl4) andhexane (C6H14) were used as precursors for silicon and carbon for theSiC coating on Co nanopowders. The unit has two precursor dosingdevices. One of the top doses—CoCl2—which is thermally decomposed bynitrogen plasma and reduced by hydrogen carrier gas, resulting in theformation of Co nanopowders. At a lower position, SiC14 and hexane areintroduced where they decompose to form Si and C. When theas-synthesized Co nanopowders travel down the unit, a thin layer of SiCis formed on the Co nanoparticles. An equal feed rate was maintained forall the precursors employed in the synthesis.

Cobalt nanopowders formed had an average particle size of less than 50nm. The SiC-coated Co nanoparticles had an average particles size ofabout 50 nm with a covered shell layer that is approximately 3 nm.

When mentioning MP fluids herein it will be understood to mean thealternative use of either the type one fluids or the type two fluidsmentioned above.

Referring again to FIG. 1, the system 10 further includes a device 20for pumping the fluid 14 in a fluid path 22 to form a polishing zone 24.

The system 10 further includes a holder 26 for securing the implantcomponent 4 and for moveably positioning the articulating surface 2 ofthe component 4 relative to the polishing zone 24.

The system 10 may further include a controller 28 for determining therate of material removal from the object for determining the directionand velocity of movement of the polishing zone 24 relative to theimplant component 4 and for determining the number of cycles ofpolishing required. As shown in FIG. 1, the system 10 may be in the formof a closed loop fluid delivery system. The fluid properties, such astemperature and viscosity, may be continually monitored and controlledby the system 10. The fluid 14 may be drawn out of the vessel 12.

The controller 28 may be utilized to improve form or geometry of theimplant by taking measurements of the implant, i.e. interferometricdata, and feeding this information into the controller 28 so that themagnetic field is applied only to the “high” spots that need reductionto achieve perfect form. The “high” spots may also be placed in thepolishing zone 24 for additional time to also achieve the reduction toachieve perfect form.

As shown in FIG. 1, the vessel 12 may be in the form of a MP-fluidconditioner. The conditioner 12 may be utilized to maintain the propercondition of the fluid 18. For the first type of MP-fluid theconditioner 12 may be in the form of a magnetic filter to separate themagnetic particles that have not deteriorated from those that havedeteriorated and have lost their magnetic properties. The magneticparticles that have not lost their magnetic properties will berecirculated and those that have lost their magnetic properties will beremoved. For the second type of MP-fluid the conditioner may merelymeasure the properties of the fluid and when the properties fall below aminimum level the MP-fluid may be drained and replaced.

The fluid 18 is drawn out of the vessel 12 and extruded onto, forexample and as shown in FIG. 1, a rotating spherical wheel in a thinribbon that will contact the articulating surface 2 of the implantcomponent 4. The ribbon is then removed by suction and fed back into theconditioner along fluid path 32 and through, as shown in FIG. 1, pump34.

As shown in FIG. 1, an electromagnet 36 may be located below thespherical polishing wheel 30. The electromagnetic magnet 36 may havespecially designed pole pieces 38 that extend up to the underside of theapex 40 of the wheel rim. These pole pieces 38 exert a strong localmagnetic field gradient over the upper side of the wheel 30.

When the MP-fluid 18 passes through the magnetic field, it stiffens inmilliseconds then returns to its original fluid state as it leaves thefield, again in milliseconds. This precisely controlled zone ofmagnetized fluid becomes the polishing tool. When the articulatingsurface 2 of an orthopaedic implant component 4 is placed into the fluid18 in this zone, the stiffened fluid ribbon is squeezed from itsoriginal thickness from about 2 millimeters, to about 1 millimeter. Thesqueezing results in significant sheer stress and subsequent polishingpressure over the section of the articulating surface 2 of theorthopaedic implant 6. At the same instant, the MP-fluid 18 conforms tothe local curvature of the implant component 4 being polished.

According to the present invention and referring now to FIG. 1A, anotherembodiment of the present invention is shown as system 10A. System 10Ais similar to system 10 of FIG. 1, but additionally includes surfacefinish feedback control loop 11A. Control loop 11A monitors the surfacefinish of the articulating surface 2 of the implant component 2 andprovides feedback for the controller 28A to control the system 10A. Theloop 11A includes a light source 13A in the form of, for example, alaser that is used to direct an incoming beam 15A onto the articulatingsurface 2 of the implant component 4. The incoming beam 15A from thelight source 13A is reflected by the articulating surface 2 of theimplant component 4 and is redirected as a reflection beam 17A to alight meter 19A in the form of, for example, an optical processor.

The light meter 19A determines the intensity or strength of thereflected beam 17A. The difference of the intensity of the beam 15A fromthe light source 13A and the intensity of the beam 17A, which isreflected from the articulating surface 2, measures the reflectivity,which is a measure of the surface finish of the articulating surface 2.The information from the light meter 19A is transmitted to thecontroller 28A and is used to determine the current surface finish ofthe articulating surface 2.

Interferometry is a traditional technique in which a pattern of brightand dark lines (fringes) result from an optical path difference betweena reference and a sample beam. The incoming light is split inside aninterferometer, one beam going to an internal reference surface and theother to the sample. After reflection, the beams recombine inside theinterferometer, undergoing constructive and destructive interference andproducing the light and dark fringe pattern. A precision translationstage and a CCD camera together generate a 3D interferogram of theobject that is stored in the computer memory. This 3D interferogram ofthe object is then transformed by frequency domain analysis into aquantitative 3D image providing surface structure analysis. Suchinterferometry systems are available from Zygo Corporation, Middlefield,Conn.

Referring now to FIG. 1B, yet another embodiment of the presentinvention is shown as system 10B. The system 10B of FIG. 1B is similarto the system 10 of FIG. 1, except that the system 10B includes acontrol loop 11B for utilizing the magnetic properties of the metallicsubstrate of the articulating surface 2 of the prosthesis 4 that ispolished. Control loop 11B includes, for example, a magnetic generatingdevice, for example an electromagnetic coil 13B, which is positionedadjacent the articulating surface 2 of the prosthesis 4.

The electromagnetic coil 13B is connected to power source 15B as well asto controller 28B. The control loop 11B is used to adjust the magneticfield generated by the electromagnetic coil 13B in response toparameters received by the controller 28B from the surface measuringdevice 17B in response to the progress of the polishing of thearticulating surface 2 of the prosthesis component 4. By utilizing thecontrol loop 11B, the magnetic properties of the metallic substrate ofthe prosthetic component 4 may be used to influence the polishingprocess in the system 10B of FIG. 1B.

Referring now to FIG. 1C, yet another embodiment of the presentinvention is shown as system 10C. System 10C is similar to system 10 ofFIG. 1, except that system 10C further includes a control loop 11C,which is utilized to utilize the higher thermal conductivity of themetal orthopaedic implant component 4 to heat the substrate of component4. The localized heating of the articulating surface 2 of theorthopaedic implant 4 will influence the removal rate of material fromthe surface 2 and thus reduce the polishing time to polish thearticulating surface 2 of the prosthetic component 4.

The control loop 11C, as shown in FIG. 1C, may include a power source13C, which is utilized to heat a warming device, for example inductioncoil 15C. The induction coil 15C is connected to controller 28C, whichis utilized to control the system 10C. The controller 28C takes inputfrom, for example, sensor 17C on surface 2 of prosthesis 4 and send theinput to the system 10C to determine the optimum amount of heating ofthe articulating surface 2 of the prosthesis 4 and thereby turns theinduction coil 15C on and off so that the articulating surface 2 of theprosthesis 4 has the ideal temperature to optimize polishing.

According to the present invention and referring now to FIG. 1D, anotherembodiment of the present invention is shown as system 10D. The system10D is similar to the system 10 of FIG. 1, except that the system 10Dfurther includes a control loop 11D, which utilizes the electricalconduction properties of a metallic prosthetic component to be anindicator of the surface finish and polishing progression of the system10D.

For example, and as shown in FIG. 1D, the system 10D may include thecontrol loop 11D. The control loop 11D may include an electrical contact13D. While a solitary electrical contact 13D may be sufficient as shownin FIG. 1D, the control loop 11D may also include a plurality ofelectrical contacts 13D. The electrical contacts 13D may be any type ofcontact, particularly a contact that may be cooperative with a rotatingor moving articulating surface.

For example, as shown in FIG. 1D, the electrical contact 13D may be inthe form of brushes. For example, the brushes may be carbon fiberbrushes or may be metal brushes. The electrical contacts 13D areconnected to a device for measuring electricity, for example aconductivity meter 15D. The conductivity meter 15D is connected to thecontroller 28D. The measure of the conductivity from the conductivitymeter 15D may be used as an indicator of the surface finish of thearticulating surface 2 and this feedback may be transferred to thecontroller 28D to be used in determining the proper processing limitsand operations of the system 10D.

According to the present invention and referring now to FIG. 1E, anotherembodiment of the present invention is shown as system 10E. System 10Eis similar to system 10 of FIG. 1, but additionally includes firstpolishing fluid particle build-up feedback control loop 11E. Controlloop 11E monitors the amount of particles that are suspended in thepolishing fluid and provides feedback for the controller 28E to controlthe system 10E. The first polishing fluid particle build-up feedbackcontrol loop 11E utilizes an optical method of measuring the suspendedparticles.

The loop 11E includes a light source 13E in the form of, for example, alaser that is used to direct an incoming beam 15E onto the surface 2E ofthe fluid in the vessel 22E. The incoming beam 15E from the light source13E is reflected by the surface 2 of the fluid in the vessel 22E and isredirected as a reflection beam 17E to a light meter 19E in the form of,for example, an optical processor.

The light meter 19E determines the intensity or strength of thereflected beam 17E. The difference of the intensity of the beam 15E fromthe light source 13E and the intensity of the beam 17E, which isreflected by the surface 2E of the fluid in the vessel 22E, measures thereflectivity, which is a measure of the suspended content of the fluidin the vessel 22E. The information from the light meter 19E istransmitted to the controller 28E and is used to determine when thefluid has excessive debris content.

It should be appreciated that, alternatively, a system 11E may utilizethe light source 13E and a meter 19E to measure either the turbidity orthe absorption of the fluid in the vessel 22E. The difference in theintensity of the beam 15E from the light source 13E and the intensity ofthe beam 17E, which travels through MP-fluid in vessel 22E and throughtransparent window (not shown), measures the absorption of the MP-fluidin the vessel 22E. The information from light meter 19E is transmittedto controller 28E.

It should be appreciated that to minimize the build-up of metalparticles in the vessel 22E, a metal separating filter 23E could be usedto constantly remove metal particles from the vessel 22E. The meter 19Eand the controller 28E can be used to control the operation of thefilter 23E.

For the first type of MP-fluid the metal separating filter 23E may be inthe form of a magnetic filter to separate the magnetic particles thathave not deteriorated from those that have deteriorated and have losttheir magnetic properties. The magnetic particles that have not losttheir magnetic properties will be recirculated and those that have losttheir magnetic properties will be removed. For the second type ofMP-fluid the metal separating filter 23F may be replaced with a deviceto measure the properties of the fluid and when the properties fallbelow a minimum level the MP-fluid may be drained and replaced.

According to the present invention and referring now to FIG. 1F, anotherembodiment of the present invention is shown as system 10F. System 10Fis similar to system 10 of FIG. 1, but additionally includes secondpolishing fluid metal particle build-up feedback control loop 11F.Control loop 11F monitors the amount of metal particles that aresuspended in the polishing fluid and provides feedback for thecontroller 28F to control the system 10F. The second polishing fluidmetal particle build-up feedback control loop 11F utilizes an electricalconductivity method of measuring the suspended metal particles. The Loopmeasures the electrical conductivity of the fluid in vessel 22F todetermine the amount of metal in the fluid in vessel 22F.

For example, and as shown in FIG. 1F, the system 10F may include thecontrol loop 11F that may include first and second electrical contacts13F and 33F, respectively, suspended in the fluid in the vessel 22F.While a solitary electrical contact 13D or 33F may be sufficient, asshown in FIG. 1F, the control loop 11F may also include a plurality ofelements to form the electrical contacts 13F and 33F. The electricalcontacts 13F and 33F may be any type of contacts, particularly contactsthat may be cooperative with a fluid.

The first electrical contact 13F is connected to an electrical powersource 25F. The second electrical contact 33F is connected to a devicefor measuring electricity, for example a conductivity meter 15F. Theconductivity meter 15F is connected to the controller 28F. The measureof the conductivity from the conductivity meter 15F may be used as ameasure of the suspended metal content of the fluid in the vessel 22F.The information from the conductivity meter 15F is transmitted to thecontroller 28F and is used to determine when the fluid has excessivemetal content.

It should be appreciated that to minimize the build-up of metalparticles in the vessel 22F, a metal separating filter 23F could be usedto constantly remove metal particles from the vessel 22F. The meter 15Fand the controller 28F can be used to control the operation of thefilter 23F.

For the first type of MP-fluid the metal separating filter 23F may be inthe form of a magnetic filter to separate the magnetic particles thathave not deteriorated from those that have deteriorated and have losttheir magnetic properties. The magnetic particles that have not losttheir magnetic properties will be recirculated and those that have losttheir magnetic properties will be removed. For the second type ofMP-fluid the metal separating filter 23F may be replaced with a deviceto measure the properties of the fluid and when the properties fallbelow a minimum level the MP-fluid may be drained and replaced.

While the systems 10, 10A, 10B, 10C, 10D, 10E and 10F of FIGS. 1-1F maybe satisfactory for polishing a convex surface, it should be appreciatedthat additional surfaces with varying shapes may well be compatible withthe system of the present invention. For example, other orthopaedicimplant's articulating surfaces, such as planar surfaces and concavesurfaces, may benefit from the polishing by a system of the presentinvention.

For example, and referring now to FIG. 2, a flat or planar articulatingsurface 6 of an orthopaedic implant 8 may be polished with the use ofsystem 100 of FIG. 2. FIG. 2 is a schematic drawing of the polishingsystem 100, which may be operated according to the present invention. Acylindrical vessel 110 contains MP-fluid (MP-fluid) 112. In a preferredembodiment, the MP-fluid 112 contains an abrasive. The vessel 110 ispreferably constructed of a non-magnetic material, which is inert to theMP-fluid 112.

In FIG. 2, vessel 110 has semi-cylindrically shaped, cross-section, andhas a flat bottom. However, the particular shape of the vessel 110 maybe modified to suit the work piece to be polished, as we described ingreater detail.

An instrument 114, such as a blade, is mounted into vessel 110 toprovide continuous stirring of the MP-fluid 112 during polishing.Orthopaedic component, for example tibial tray 8, is connected to arotatable work piece spindle 116. The work piece spindle 116 ispreferably made of a non-magnetic material. The work piece spindle 116is mounted on a spindle slide 118 and can be moved in a verticaldirection. Spindle slide 118 may be driven by a conventional servomotor,which operates according to electrical signals from a programmablecontrol system 120.

The rotation of vessel 110 is controlled by vessel spindle 122, which ispreferably positioned in a central location below vessel 110. Vesselspindle 122 can be driven by a conventional motor or by other powersource.

An electromagnet 124 is positioned adjacent to vessel 110 so as to becapable of influencing the MP-fluid 112 in a region containing theorthopaedic implant 8. The electromagnet 124 should be capable ofinducing a magnetic field sufficient to carry out the polishingoperation, and may, for example, include a magnetic field of at leastabout 100 ka per meter. The electromagnet 124 is activated by winding126 from a power supply unit 128, which is connected to control system120. The winding 126 can be any conventional magnetic winding. Theelectromagnet 124 is set up on an electromagnet slide 130 and can bemoved in a horizontal direction, preferably along the radius of vessel110. It should be appreciated that the strength of magnetic force neededfor the particles may be different when utilizing the first typeMP-fluid from that used when utilizing the second type MP-fluid.

Electromagnetic slide 130 may be driven by a conventional servomotor,which operates according to electrical signals from the programmablecontrol system 120.

The winding 126 is activated by power supply unit 128 during polishingto induce a magnetic field and influence the MP-fluid 112. Preferably,the MP-fluid 112 is acted on by a non-uniform magnetic field in a regionadjacent to the orthopaedic implant 8. In this embodiment, equalintensity lines of the field are normal, or perpendicular, to thegradient of the field. The force of the magnetic field is a gradientdirected toward the vessel bottom and normal to the surface of theorthopaedic implant 8. Application of the magnetic field from theelectromagnet 124 causes the MP-fluid 112 to change its viscosity andplasticity in a limited polish zone 132 adjacent to the surface beingpolished. It should be appreciated that the strength of magnetic forceneeded for the particles may be different when utilizing the first typeMP-fluid from that used when utilizing the second type MP-fluid.

The size of the polishing zone 132 is defined by the gap between thepole pieces of the electromagnet 124 and the shape of the tips of theelectromagnet 124. Abrasive particles in the MP-fluid are preferablyacted upon by the MP-fluid substantially only in the polishing zone 132and the pressure of the MP-fluid against the surface of the orthopaedicimplant 8 is largest in the polishing zone 132.

The composition of the MP-fluid 112 used in the method and devicesdiscussed herein is preferably as described in U.S. Pat. No. 5,449,313.The MP-fluid may include a plurality of magnetic particles, abrasiveparticles, a stabilizer, and a carrying fluid selected from the groupconsisting of water and glycerin. The magnetic particles (preferablycarbonyl iron particles) are coated with a protective layer of a polymermaterial, which inhibits their oxidation. The protective layer ispreferably resistant to mechanical stress, and as thin as practical. Ina preferred embodiment, the coating may be PTFE (Teflon). The particlesmay be coated by the usual process of micro-capsulization.

The polishing machine, as shown in FIG. 2, can operate as follows. Theorthopaedic implant 8 is coupled to workplace spindle 116 in position byspindle slide 118 at a clearance h, with respect to the bottom of thevessel 110 so that, preferably, a portion of the orthopaedic implant 8to be polished is immersed in the MP-fluid 112. The clearance h may beany suitable clearance that will permit polishing of the work piece. Theclearance h will affect the material removal rate for the orthopaedicimplant 8. The clearance h will also affect the size of the contact spotat which the polishing zone 132 contacts the orthopaedic implant 8.

The clearance h is preferably chosen so that the surface area of thecontact spot is less than ⅓ of the surface area of the orthopaedicimplant 8. The clearance h may be changed during the polishing process.

The orthopaedic implant 8 and the vessel 110 may both be rotated. Forexample, the orthopaedic implant 8 and the vessel 110 may be rotatedopposite to each other. The vessel spindle 122 is put into rotatingmotion, thereby rotating the vessel 110. The vessel spindle 122 rotatesabout a central axis and preferably rotates vessel 110 at a speedsufficient to affect polishing, but insufficient to generate acentrifugal force sufficient to substantially spin or spray the MP-fluid112 out of the vessel 110.

The vessel 110 may be rotated at a constant velocity. The motion of thevessel 110 provides continuous delivery of a fresh portion of theMP-fluid 112 to the region where the orthopaedic implant 8 is locatedand provides continuous motion of the MP-fluid 112 in contact with thesurface of the orthopaedic implant being polished in the polishing zone132. It should be appreciated that additional carrying fluid, preferablywater or glycerin, is added during the polishing to replenish carryingfluid that has vaporized, thus maintaining the properties of the fluid.

The work piece spindle 116 may also be rotated about a central axis toprovide rotating movement to the orthopaedic implant 8. The work piecespindle 116 operates in speeds, for example up to 2,000 RPM, with about500 RPM being typical. The motion of the work piece spindle 116continuously brings a fresh part of the surface of the orthopaedicimplant 8 into contact with the polishing zone 132, so that materialremoval along the circumference of the surface being polished will besubstantially uniform.

As abrasive particles in the MP-fluid 112 contact the surface 6 of theorthopaedic implant 8, a re-shaped area having the width of thepolishing zone is gradually polished on the surface 6 of the orthopaedicimplant 8. Polishing is accomplished in one or more cycles, with anincremental amount of material removed from the orthopaedic implant ineach cycle. The polishing zone moves through the ring-shaped area onceduring each cycle as the orthopaedic implant is rotated. Polishing ofthe whole surface of the orthopaedic implant 8 is achieved by radialdisplacement of the electromagnet 124 using the electromagnet slide 130,which causes the polishing zone 132 to move relative to the work piecesurface.

Referring now to FIG. 3, yet another embodiment of the present inventionis shown as system 200. System 200 is similar to the system 100 of FIG.2, except that the system 200 is adapted for highly efficient polishingof convex work pieces. For example, and as shown in FIG. 3, the system200 is adapted for use with, for example, work piece 4 in the form of anorthopaedic hip head. As shown in FIG. 3, the system 200 includes avessel 262, which is in the form of a circular cup. The radius ofcurvature of the internal wall adjacent to polishing zone 232 is largerthan the largest radius of curvature of the orthopaedic component 4.

During polishing, it is desirable to minimize the movement of MP-fluid212 relative to the vessel 262. To minimize the movement or slippage ofthe MP-fluid 212, the internal wall of the vessel 262 may be coveredwith a layer of a nap of porous material 215 to provide reliablemechanical adhesion between MP-fluid 212 and the wall of the vessel 262.Work piece spindle 216 is connected with spindle slide 218, which isconnected to rotatable table 236. The rotatable table 236 is connectedto a table slide 237.

Spindle slide 218, rotatable table 236, and table slide 237 may bedriven by conventional servomotors, which operate according toelectrical signals from programmable control system 220. Rotatable table236 permits work piece spindle 216 to be continuously rotated about itshorizontal axis 219, or permits its positioning at an angle α with theinitial vertical axis 221 of spindle 216. The horizontal axis 219preferably is located at the center of curvature f the polished surfaceat the initial vertical position of the work piece spindle 216.

Spindle slide 218 permits vertical displacement h′ of the center of thepolished surface curvature relative to axis 219. Table slide 237 movesthe rotatable table 236 with spindle slide 218 and work piece spindle216 to obtain and maintain the desired clearance h between the polishedsurface of the work piece or orthopaedic implant 4 and the bottom of thevessel 262.

An electromagnet 224 may be stationary and positioned below the vessel262 such that its magnetic gap is symmetric about the work piece spindleaxis 221 when this axis is perpendicular to the plane of the polishingzone 232. It should be appreciated that the strength of magnetic forceneeded for the particles may be different when utilizing the first typeMP-fluid from that used when utilizing the second type MP-fluid.

The polishing machine for the system 200 as shown in FIG. 4 operates asfollows. To polish the orthopaedic implant 4, work piece spindle 216with attached orthopaedic implant 4 is positioned so that the center ofthe radius of curvature of the orthopaedic implant 4 is brought intocoincidence with the pivotal point or rotation of axis 219 of therotatable table 236. The removal rate for the orthopaedic implant to bepolished is then determined experimentally using a test work piecesimilar to the orthopaedic implant to be polished. Polishing of theorthopaedic implant 4 may then be conducted automatically by moving itssurface relative to the polishing zone 232 using rotatable table 236(see FIG. 3) which rocks work piece spindle 216 and changes the angle αaccording to calculated regimes of treatment.

Referring now to FIG. 5, yet another embodiment of the present inventionis shown as system 300. System 300 is similar to system 200 of FIG. 3,except that system 300 includes a vessel 310 that has an additionalring-shaped trough 309, which passes through gap 311 of electromagnet324. It should be appreciated that the strength of magnetic force neededfor the particles may be different when utilizing the first typeMP-fluid from that used when utilizing the second type MP-fluid. Thisconfiguration of the internal wall of the vessel 310 results in asmaller, more focused, polishing zone 332. The configuration alsoresults in an increase in adhesion between the MP-fluid 312 and thevessel 310. The smaller, more focused, polished zone results in asmaller contact spot. In all other respects, the embodiment depicted inFIG. 5 is the same as that depicted in FIG. 3.

Referring now to FIG. 6, yet another embodiment of the present inventionis shown as system 400. System 400 is similar to system 100 of FIG. 2,except that the system 400 allows for multiple objects to be polishedsimultaneously, thereby increasing the productive capacity of thesystem. For the system 400, as shown in FIG. 6, an MP-fluid 412 isplaced into a cylindrical vessel 410. Orthopaedic implants to bepolished in the form of, for example tibial trays 4A and 4B or otherorthopaedic implants with a planar surface to polish, are fixed onspindles, for example as shown, a first orthopaedic implant 4A is placedon first spindle 416A and similarly a second orthopaedic implant 4B isplaced on second spindle 416B. The spindles 416A and 416B are mounted ona disc 423 capable of rotating in the horizontal plane. An electromagnet424 is installed under the vessel 410 such that it creates a magneticfield along the entire surface of the vessel 410. It should beappreciated that the strength of magnetic force needed for the particlesmay be different when utilizing the first type MP-fluid from that usedwhen utilizing the second type MP-fluid.

Disc 423, vessel 410 and the orthopaedic implants to be polished 4A and4B are put into rotation in the same or opposite directions with equalor different speeds. By regulating the magnetic field intensity and therotation of the disc, the vessel and the objects, the rate of removal ofmaterial from the surface of the object to be polished is controlled.

Referring now to FIGS. 7, 8 and 9, the system 10 is shown in the form ofa polishing machine adapted for polishing convex articulating surfacesof orthopaedic implants. The polishing machine 10, as shown in FIG. 7,includes a work piece spindle 17 for securing the orthopaedic implantcomponent 4. The polishing machine 10 further includes a spherical wheel30 to which the fluid path 22 is directed. Fluid from fluid conditioner12 is pumped by pump 20 along fluid path 22 to polishing zone 24adjacent the articulating surface 2 of the orthopaedic implant 4. Aspindle slide 18 advances the orthopaedic implant 4 into contact withthe polishing zone 24 to commence the polishing of the articulatingsurface 2 of the orthopaedic implant 4.

Referring now to FIGS. 8 and 9, the polishing zone 24 is shown ingreater detail. The fluid path 22 extends from the pump 20 to thepolishing zone 24. The polishing zone 24 is adjacent the articulatingsurface 2 of the orthopaedic implant 4. A work piece spindle 17 is used,as shown in FIGS. 8 and 9, to rotate the orthopaedic implant 4 aboutvertical axis 21. It should be appreciated that the vertical axis 21 maybe changed to accommodate the external convex periphery of thearticulating surface 2 of the orthopaedic implant 4. The work piecespindle 17, as shown in FIG. 8, may rotate in the direction of arrows 11about centerline 21 to obtain a different angle(s) 0 of the orientationof the work piece spindle 17 with respect to the vertical axis.

Referring now to FIG. 10, the orthopaedic implant in the form oforthopaedic component 4 is shown in greater detail. The orthopaediccomponent 4 is in the form of a convex orthopaedic implant in the formof a head 6. The head 6 has a generally spherical articulating surface5. The prosthetic component, as shown in FIG. 10, is in the form of hipstem 9. The hip stem 9 includes a stem portion 7 to which head 6 may beremovably attached.

Referring now to FIG. 11, the hip stem 9 is shown in connection with acup 3 to form a hip prosthesis 5. The hip prosthesis 5 includes the hipstem 9 as well as cup 3.

Referring now to FIG. 12, yet another embodiment of the presentinvention is shown as system 500. System 500 is adapted for use inpolishing concave surfaces. For example, the system 500 is suitable forpolishing the articulating surface 11 of cup 3 of a hip cup prosthesis.It should be appreciated that the system 500 may also be used to polishconcave surfaces of vertebral implants such as those of FIGS. 18 and 18Aor glenoid components. The system 500 is somewhat similar to the system100 of FIGS. 1, 7, 8, and 9, except that the system 500 utilizes a ball530 to replace the spherical drum wheel 30 of the system 10.

The system 500 includes a fluid conditioner 512 for receiving MP-fluid518. The fluid 518 is caused to flow by pump 520 along fluid path 522 topolishing zone 524 adjacent the articulating surface 11 of the cup 3.The fluid path 522 includes a path through internal cavities 540 of theball 530. The ball 530, as shown in FIG. 12, includes a plurality ofopenings or slits 542, which permit the MP-fluid 518 to pass from theinternal cavities 540 of the ball 530 to the polishing zone 524.

Preferably, as shown in FIG. 12, the ball 530 rotates in the directionof arrow 544 while the cup 3 is located and mounted on spindle 517,which rotates in the direction of arrow 546. The spindle 517 preferablyrotates opposed to the direction of rotation 544 of the ball 530. Thespindle 517, as shown in FIG. 12, may be permitted to translatevertically by means of spindle slide 519. While the ball 530 maysuccessfully polish the cup 3 without any angular motion between the cup3 and the ball 530, preferably and as shown in FIG. 12, the spindle 517is able to rotate in the direction of arrow 518 about origin 508 to formangle θ such that an additional portion of the ball 530 may bepositioned within the inner-concave periphery of the cup 3. The rotationof the spindle 517 about origin 508 is accomplished by mounting thespindle 517 to a rotating head 506 that in turn is mounted on spindleslide 519. Thus, the cup 3 can be exposed to more surfaces forpolishing.

The angular rotation of the cup 3 relative to the ball 530 may beaccomplished by a combination of vertical movements of the spindle slide519 and horizontal motions of table slide 537 as well as by rotation ofthe rotating head 506. The ball 530 moving horizontally with the tableslide 537 in the spindle and the cup 3 moving vertically with thespindle slide 519 and rotating with the rotating head 506. The relativemotions of the spindle slide 519 and table slide 537 may for example, becontrolled by controller 528. Similarly, the pump 520 as well as therotation of the ball 530 and the spindle 517, may be controlled bycontroller 528.

The system 500 of FIG. 12 preferably includes a magnetic field forpermitting the MP-fluid 518 to act as described in the presentinvention. For example, and as shown in FIG. 12, the ball 530 may actas, for example, a north pole and south pole 525 may be utilized in aspaced apart relationship from the ball 530. Alternatively, the magneticpoles may be spaced from the ball 530. For example, a first externalpole working as a north pole may be in the form of pole 525C as shown inphantom. The second or south magnetic pole 525 may be positioned in aspaced apart relationship from the first magnetic pole 525C.Alternatively, a pair of magnetic poles, such as south magnetic pole525S and north magnetic pole 525N may, as show in phantom, be locatedwith the ball 530. It should be appreciated that the strength ofmagnetic force needed for the particles may be different when utilizingthe first type MP-fluid from that used when utilizing the second typeMP-fluid.

Referring now to FIG. 12A, yet another embodiment of the presentinvention is shown as system 500A. The system 500A is adapted for use inpolishing concave surfaces and it similar to the system 500 of FIG. 12.The system 500A is suitable for polishing the articulating surfaces ofconcave surfaces, for example, the articulating surface 11 of cup 3 of ahip cup prosthesis. The system 500A is somewhat similar to the system500 of FIGS. 1, 7, 8, and 9, except that the system 500A utilizes a ball530A to replace the spherical drum wheel 30 of the system 10. The system500A uses a fluid conditioner 512A for receiving MP-fluid 518A.

For the first type of MP-fluid the conditioner 512A may be in the formof a magnetic filter to separate the magnetic particles that have notdeteriorated from those that have deteriorated and have lost theirmagnetic properties. The magnetic particles that have not lost theirmagnetic properties will be recirculated and those that have lost theirmagnetic properties will be removed. For the second type of MP-fluid theconditioner may merely measure the properties of the fluid and when theproperties fall below a minimum level the MP-fluid may be drained andreplaced.

The fluid 518A is caused to flow by pump 520A along fluid path 522A topolishing zone 524A adjacent the articulating surface 11 of the cup 3.The fluid path 522A includes a path through internal cavities 540A ofthe ball 530A. The ball 530A, as shown in FIG. 12A, includes a pluralityof openings or slits 542A that, as shown in FIG. 12A, are generallyhorizontal. The slits 542A permit the MP-fluid 518A to pass from theinternal cavities 540A of the ball 530A to the polishing zone 524A.

Preferably, and as shown in FIG. 12A, the ball 530A rotates in thedirection of arrow 544A, while the cup 3 is located and mounted onspindle 517A. The spindle 517A rotates in the direction of arrow 546A.The spindle 517A preferably rotates opposed to the direction of rotation544A of the ball 530A. The spindle 517A, as shown in FIG. 12A, may bepermitted to translate vertically by means of spindle slide 519A.

While the ball 530A may successfully polish the cup 3 without anyangular motion between the cup 3 and the ball 530A, preferably and asshown in FIG. 12A, the spindle 517A is able to rotate in the directionof arrow 518A about origin 508A to form angle θ′ such that an additionalportion of the ball 530A may be positioned within the inner-concaveperiphery of the cup 3. The rotation of spindle 517A about origin 508Ais accomplished by mounting the spindle 517A to rotating head 506A thatin turn is mounted on spindle slide 519A. Thus, the cup 3 can be exposedto more surfaces for polishing.

The angular rotation of the cup 3 relative to the ball 530A may beaccomplished by a combination of vertical movements of the spindle slide519A and the horizontal motions of table slide 537A, as well as byrotation of the rotating head 506A. The ball 530A moving horizontallywith the table slide 537A and the spindle 517A, and the cup 3 movingvertically with the spindle slide 519A and rotating with the rotatinghead 506A. The relative motion of the spindle slide 519A and the tableslide 537A may, for example, be controlled by controller 528A.Similarly, the pump 520A, as well as the rotation of the ball 530A andthe spindle 517A, may be controlled by controller 528A.

To properly excite the MP-fluid, the MP-fluid 518A is affected by amagnetic field. Such magnetic field may be accomplished in any suitablemanner. For example, and as shown in FIG. 12A, the ball 530A may form asa magnet, for example, a north pole. The system 500A may further includea south or second magnetic pole 525A positioned spaced from the ball530A to provide a magnetic field between the north and south poles 530Aand 525A respectively. It should be appreciated that the strength ofmagnetic force needed for the particles may be different when utilizingthe first type MP-fluid from that used when utilizing the second typeMP-fluid.

Alternatively, the MP-fluid 518A may be exposed to a magnetic field by apair of north and south magnetic fields external to the ball 530A. Forexample, as shown in FIG. 12A, a second north magnetic pole 525B and thesouth pole 525A may be used. Alternatively, a pair of magnetic polessuch as south magnetic pole 525SS and north magnetic pole 525NN may, asshown in phantom, be located within the ball 530A.

Referring now to FIG. 13, yet another embodiment of the presentinvention is shown as system 600. The system 600 is similar to thesystem 100 of FIG. 1, except that the spherical drum 30 of the system100 is replaced with a generally cylindrical lapping wheel 630. Thelapping wheel 630 is rotated by a spindle (not shown) and used toprovide a lapping surface with recessed surface 15 of tibial tray 8.Tibial tray 8 includes recessed surface 15, which must be polished. Apolishing of the recessed surface 15 is quite troublesome in that toolsare not generally available to polish the surface 15. The lapping wheel630 is caused to translate vertically by vertical slide 619 as well ashorizontally by horizontal slide 625. MP-fluid 618 conditioned by fluidconditioner 612 is pumped by pump 620 through conduit 622 to polishingzone 632.

For the first type of MP-fluid the conditioner 612 may be in the form ofa magnetic filter to separate the magnetic particles that have notdeteriorated from those that have deteriorated and have lost theirmagnetic properties. The magnetic particles that have not lost theirmagnetic properties will be recirculated and those that have lost theirmagnetic properties will be removed. For the second type of MP-fluid theconditioner may merely measure the properties of the fluid and when theproperties fall below a minimum level the MP-fluid may be drained andreplaced.

Referring now to FIG. 13A, yet another embodiment of the presentinvention is shown as system 700. System 700 is similar to system 100 ofFIG. 2, except that a lapping wheel 730 is positioned between vessel 712and work piece in the form of tibial tray 8. The lapping wheel 730 drawsMP-fluid 718 from the vessel 712 and applies the fluid 718 to polishingzone 732 between the articulating surface 6 of the tibial tray 8 andwheel 730.

A spindle 717 rotates the tibial tray 8 while a horizontal slide 725advances the lapping wheel 730 horizontally and a vertical slide 719permits the movement of the slide vertically. A controller 728 controlsthe motion of the horizontal slide 725, the vertical slide 719, thespindle 717 as well as the lapping wheel 730 to properly lap thearticulating surface 6 of the tibial tray 8.

Referring now to FIG. 13B, yet another embodiment of the presentinvention is shown as system 800. The system 800 is similar to thesystem 700 of FIG. 13A, but includes lapping wheel 830 that is largerand diameter and narrower than the lapping wheel 730 of the system 700.Again, a tibial tray 8 has its articulating surface 6 polished by thelapping wheel 830. MP-fluid 818 from the vessel 812 is advanced by thelapping wheel 830 to the polishing zone 832 where the MP-fluid 818 isutilized to lap the articulating surface 6. A horizontal slide 825 and avertical slide 819 are utilized to position the lapping wheel 830 aboutthe articulating surface 6. A controller 828 is used to control thepositioning of the vertical slide 819, the horizontal slide 825, thespindle 817, and the lapping wheel 830.

According to the present invention, and referring now to FIG. 14, yetanother embodiment of the present invention is shown as system 900. Thesystem 900 is similar to the system 800 of FIG. 13B, except that lappingwheel 930 is mounted vertically and that the lapping wheel 930 is smallin diameter. The system 900 provides for lapping at the end of thelapping wheel 930. The lapping wheel 930 is positioned in vessel 912,which is filled with MP-fluid 918. Horizontal slide 925 and verticalslide 919 are controlled by controller 928, which also controls therotation of the lapping wheel 930 and the work piece spindle 917.

Referring now to FIG. 15, tibial tray 8 is shown in greater detail. Thetibial tray 8 includes the recessed surface 6, which is polishable bythe polishing system of the present invention.

Referring now to FIGS. 16 and 17, yet another prosthetic component to bepolished by the system of the present invention is shown as tibial tray50. The tibial tray 50 includes an articulating surface 52. The surface52, as shown in FIGS. 16 and 17, is planar. Therefore, the system, suchas system 100 of FIG. 2, is suitable for polishing the articulatingsurface of the tibial tray 50 of FIGS. 16 and 17.

Referring now to FIG. 17A, yet another embodiment of the presentinvention is shown as system 900F. The system 900F is adapted for use inpolishing planar surfaces, for example, knee tibial surfaces. The system900F is somewhat similar to the system 100 of FIG. 2. The system 900Fincludes a vessel 910F for storing the MP-fluid 918F. The bearingsurface of the knee tibial component 3 is immersed in the MP-fluid 918Fin the vessel 910F.

Preferably, and as shown in FIG. 17A, the knee tibial component 3rotates in the direction of arrow 946F. The vessel 910F rotates in thedirection of arrow 944F. The knee tibial component 3 preferably rotatesin a direction opposed to the direction of rotation 944F of the vessel910F.

System 900F of FIG. 17A further includes components capable of providinga magnetic field for the MP-fluid 918F. For example, the system 900F mayinclude magnets such as those of FIG. 18C, the magnets may, for example,be electromagnetic magnets. It should be appreciated that the strengthof magnetic force needed for the particles may be different whenutilizing the first type MP-fluid from that used when utilizing thesecond type MP-fluid.

Referring now to FIG. 18, yet another prosthesis that may be polished bythe systems of the present invention, is shown as vertebral disc 56. Thevertebral disc 56 includes a central component 58 and opposed endportions 60. The end portions 60 contact vertebrae 13 and the centerportion 58 provides for the articulation of the vertebral artificialdisc 56.

The central portion 58 includes a pair of opposed concave surfaces 62while the end portions 60 include convex articulating surfaces 64. Theconcave surfaces 62 are suitable for being polished by the system 500 ofFIG. 12 or the system 900C of FIG. 18C, while the convex surfaces 64 ofthe end portions 60 are suitable for polishing by, for example, thesystem 10 of FIG. 1 or the system 900B of FIG. 18B.

Referring now to FIG. 18A, yet another prosthesis that may be polishedby the system of the present invention is shown as Charite'® vertebraldisc 56A. The vertebral disc 56A includes a central component 58A andopposed end portions 60A. The end portions 60A contact vertebrae 13 andthe center portion 58A provides for articulation of the Charite'®vertebral artificial disc 56A.

The central portion 58A includes a pair of opposed convex surfaces 62A,while the end portions 60A include concave articulating surfaces 64A.The convex surfaces 62A and the concave articulating surfaces 64Ainclude portions 65A that are substantially linear as well. The convexsurfaces 62 of the central portion 58 are suitable for being polished bythe system 10 of FIG. 1 or by system 900B of FIG. 18B. The concavesurfaces 64A of the end portions 60A are suitable for polishing by, forexample, the system 500 of FIG. 12 or the system 900C of FIG. 18C.

Referring now to FIG. 18B, yet another embodiment of the presentinvention is shown as system 900B. The system 900B is similar to thesystem 100 of FIG. 2, except that the system 900B is adapted for highlyefficient polishing of convex work pieces. For example, the system 900may be adapted for use in polishing convex articulating surfaces ofvertebral implants, such as those described in FIGS. 18 and 18A.

For example, and as shown in FIG. 18B, the system 900B is adapted foruse with, for example, work piece 909B in the form of a vertebralcomponent. As shown in FIG. 18B, the system 900B includes a vessel 922B,which is in the form of a circular cup. The radius of curvature of theinternal wall adjacent to the polishing zone (not shown) is larger thanthe largest radius of curvature of the vertebral component 909B.

During polishing, it is desirable to minimize the movement of theMP-fluid 912B relative to the vessel 922B. To minimize the movement orslippage of the MP-fluid 912B, the internal wall of the vessel may becovered with a layer or nap of porous material A (not shown). Work piecespindle 916B is connected with spindle slide 918B, which is connected torotatable table 936B. The rotatable table 936B is connected to a tableslide 937B.

Spindle slide 918B, rotatable table 936B, and table slide 937B may bedriven by conventional servomotors, which operate according toelectrical signals from programmable control system 920B. Rotatabletable 936B permits work piece spindle 916B to be continuously rotatedabout its horizontal axis 919B, or permits its polishing at an angle α′with the initial vertical axis 921B of the spindle 916B. The horizontalaxis 919B preferably is located at the center curvature located at thecenter of curvature of the polished surface at the initial verticalposition of the work piece spindle 916B.

Work spindle slide 918B permits vertical displacement of the center ofthe polishing surface curvature relative to the horizontal axis 919B.Table slide 937B moves the rotatable table 936B with the spindle slide918B and the work piece spindle 916B to obtain and maintain the desiredclearance between the polished surface of the work piece and the bottomof the vessel 922B.

An electro magnet 924B may be stationery and positioned below the vessel922B, such as its magnetic gap is symmetric about the work piece spindleaxis 921B when this axis is perpendicular to the plane of the polishingzone.

Referring now to FIG. 18C, yet another embodiment of the presentinvention is shown as system 900C. The system 900C is adapted for use inpolishing concave surfaces, for example, vertebral concave articulatingsurfaces. The system 900C is somewhat similar to the system 500 of FIG.12, except that the system 900C utilizes a convex component 930C toreplace the ball 530 of the system 500.

The system 900C includes a fluid conditioner 912C for receiving MP-fluid918C. The fluid 918C is caused to flow along a fluid path 922C to polishzone 924C adjacent the articulating surface 11 of the vertebralcomponent 3. The fluid path 922C includes a path through internalcavities 940C of the convex component 930C. The convex component 930C,as shown in FIG. 18C, includes the plurality of tubular or cylindricalcavities 940C, which permit the MP-fluid 918C to pass to the polishingzone 924C.

For the first type of MP-fluid the conditioner 912C may be in the formof a magnetic filter to separate the magnetic particles that have notdeteriorated from those that have deteriorated and have lost theirmagnetic properties. The magnetic particles that have not lost theirmagnetic properties will be recirculated and those that have lost theirmagnetic properties will be removed. For the second type of MP-fluid theconditioner may merely measure the properties of the fluid and when theproperties fall below a minimum level the MP-fluid may be drained andreplaced.

Preferably, and as shown in FIG. 18C, the convex component 930C rotatesin the direction of arrow 944C, while the vertebral component 3 islocated and mounted on spindle 917C. The spindle 917C rotates in thedirection of arrow 946C. The spindle 917C preferably rotates opposed tothe direction of rotation 944C of the convex component 930C. The spindle917C, as shown in FIG. 18C, may be permitted to translate vertically bymeans of spindle slide 919C. While the convex component 930C maysuccessfully polish the vertebral component 3, without any angularmotion between the vertebral component 3 and the convex component 930C,preferably the spindle 917C is able to rotate about the origin with amechanism (not shown) such that additional portions of the convexcomponent 930C may be positioned within the inner concave periphery 11of the vertebral component 3. Such a mechanism is shown in FIGS. 12 and12A.

System 900C of FIG. 18C further includes components capable of providinga magnetic field for the MP-fluid 918C. For example, and as shown inFIG. 18C, the system 900C of FIG. 18C includes a first pole 925C, whichmay be a north pole. The system 900C further includes a second pole927C, which may be a south pole. The poles 925C and 927C may, forexample, be electromagnetic magnets.

Referring now to FIG. 19, yet another prosthesis that may be polished bythe system of the present invention is shown as femoral knee prosthesis72. The femoral knee prosthesis 72 includes an articulating surface 74,which includes concave as well as convex portions. The convex portionsof the articulating surface 74 are suitable for polishing by the system10 of FIG. 1 while the concave portions are suitable for polishing bythe system 500 of FIG. 12. It should be appreciated that, forsimplicity, the entire articulating surface 74 may be polished utilizingthe system 500 of FIG. 12.

Referring now to FIG. 19A, yet another embodiment of the presentinvention is shown as system 900E. The system 900E is adapted for use inpolishing articulate surfaces, for example, knee femoral surfaces. Thesystem 900E is somewhat similar to the system 10 of FIG. 1, except thatthe system 900E utilizes a reverse configuration to that of the system10 in that the knee component 3 is positioned below and a concavecomponent 930E is positioned over the knee component 3. The system 900Eincludes a fluid conditioner 912E for receiving the MP-fluid 918E. TheMP fluid 918E is caused to flow along a fluid path 922E to polish zone924E adjacent the articulating surface 11 of the knee component 3.

For the first type of MP-fluid the conditioner 912E may be in the formof a magnetic filter to separate the magnetic particles that have notdeteriorated from those that have deteriorated and have lost theirmagnetic properties. The magnetic particles that have not lost theirmagnetic properties will be recirculated and those that have lost theirmagnetic properties will be removed. For the second type of MP-fluid theconditioner may merely measure the properties of the fluid and when theproperties fall below a minimum level the MP-fluid may be drained andreplaced.

Preferably, and as shown in FIG. 19A, the concave component 930E ismounted on spindle 917E rotates in the direction of arrow 944E, whilethe knee component 3 is located below. The knee component 3 rotates inthe direction of arrow 946E. The knee component 3 preferably rotates ina direction opposed to the direction of rotation 944E of the concavecomponent 930E.

While the concave component 930E may successfully polish the kneecomponent 3, without any angular motion between the knee component 3 andthe convex component 930E, preferably the spindle 917E is able torotate, pivot or translate with a mechanism (not shown) such thatadditional portions of the knee component 3 may be positioned inalignment with the concave component 930E. Such a mechanism is shown inFIGS. 12 and 12A. Alternatively the mechanism may be a commerciallyavailable manipulator or robot (not shown).

Referring now to FIG. 20, yet another prosthesis that may be polished bythe system of the present invention is shown as glenoid prosthesis 66.The glenoid prosthesis 66 includes a concave articulating surface 68 andopposed pegs 70, which engage with glenoid 71. The articulating surface68 is adapted for polishing by the system 500 of FIG. 12.

Referring now to FIG. 20A, yet another embodiment of the presentinvention is shown as system 900D. The system 900D is adapted for use inpolishing concave surfaces, for example, glenoid implant surfaces. Thesystem 900D is somewhat similar to the system 500 of FIG. 12, exceptthat the system 900D utilizes a convex component 930D to replace theball 530 of the system 500.

The system 900D includes a fluid conditioner 912D for receiving MP-fluid918D. The fluid 918D is caused to flow along a fluid path 922D to polishzone 924D adjacent the articulating surface 11 of the glenoid component3. The fluid path 922D includes a path through internal cavities 940D ofthe convex component 930D. The convex component 930D, as shown in FIG.20A, includes the plurality of tubular or cylindrical cavities 940D,which permit the MP-fluid 918D to pass to the polishing zone 924D.

Preferably, and as shown in FIG. 20A, the convex component 930D rotatesin the direction of arrow 944D, while the glenoid component 3 is locatedand mounted on spindle 917D. The spindle 917D rotates in the directionof arrow 946D. The spindle 917D preferably rotates opposed to thedirection of rotation 944D of the convex component 930D. The spindle917D, as shown in FIG. 20A, may be permitted to translate vertically bymeans of spindle slide 919D. While the convex component 930D maysuccessfully polish the glenoid component 3, without any angular motionbetween the glenoid component 3 and the convex component 930D,preferably the spindle 917D is able to rotate about the origin with amechanism (not shown) such that additional portions of the convexcomponent 930D may be positioned within the inner concave periphery 11of the glenoid component 3. Such a mechanism is shown in FIGS. 12 and12A.

System 900D of FIG. 20A further includes components capable of providinga magnetic field for the MP-fluid 918D. For example, and as shown inFIG. 20A, the system 900D of FIG. 20A includes a first pole 925D, whichmay be a south pole. The system 900D further includes a second pole927D, which may be a north pole. The poles 925D and 927D may, forexample, be electromagnetic magnets.

Referring now to FIG. 21, yet another embodiment of the presentinvention is shown as tibial tray 76. The tibial tray 76 includes arecess surface 78, which is suitable for polishing by any of the systems600, 700 or 800 of FIGS. 13, 13A, and 13B respectively.

Referring now to FIG. 21A, yet another embodiment of the presentinvention is shown as system 900G. The system 900G is adapted for use inpolishing planar surfaces, for example, recessed knee tibial surfaces.The system 900G is somewhat similar to the system 100 of FIG. 2. Thesystem 900G includes a vessel 910G for storing the MP-fluid 918G. Thebearing surface of the recessed knee tibial component 3 is immersed inthe MP-fluid 918G in the vessel 910G.

Preferably, and as shown in FIG. 21A, a planar contacting component 965Gis mounted on spindle 917G and rotates in the direction of arrow 944G,while the recessed knee tibial component 3 is located below. Therecessed knee tibial component 3 rotates in the direction of arrow 946G.The recessed knee tibial component 3 preferably rotates in a directionopposed to the direction of rotation 944G of the planar contactingcomponent 965G.

System 900G of FIG. 21A further includes components capable of providinga magnetic field for the MP-fluid 918G. For example, the system 900G mayinclude magnets such as those of FIG. 18C. The magnets may, for example,be electromagnetic magnets.

Referring now to FIG. 22, yet another prosthesis that may be polished bythe system of the present invention is shown as shoulder prosthesis 80.The shoulder prosthesis 80 includes a head 82, which may be removablefrom the shoulder prosthesis 80. The head 82 includes a convexarticulating surface 84, which may be polished utilizing, for example,the system 10 of FIG. 1.

Referring now to FIG. 22A, yet another embodiment of the presentinvention is shown as system 900H. The system 900H is adapted for use inpolishing convex surfaces, for example, humeral head surfaces. Thesystem 900H is somewhat similar to the system 200 of FIG. 3. The system900H includes a vessel 910H for storing the MP-fluid 918H. The bearingsurface 11 of the convex humeral head component 3 is immersed in theMP-fluid 918H in the vessel 910H.

Preferably, and as shown in FIG. 22A, the vessel 910H has a concaveperiphery 965H. The vessel 910H may rotate in the direction of arrow944H. The convex humeral head component 3 may be mounted on spindle 917Hand rotates in the direction of arrow 946H. The convex humeral headcomponent 3 preferably rotates in a direction opposed to the directionof rotation 944H of the vessel 910H.

System 900H of FIG. 22A further includes components capable of providinga magnetic field for the MP-fluid 918H. For example, the system 900H mayinclude magnets such as those of FIG. 18C. The magnets may, for example,be electromagnetic magnets.

Referring now to FIG. 23, yet another embodiment of the presentinvention is shown as method 1000 for polishing an articulating surfaceof an orthopaedic implant. The method 1000 includes a first step 1010 ofcreating a polishing zone within a MP-fluid. The method 1000 furtherincludes a second step 1012 of controlling the consistency of the fluidin the polishing zone. The method 1000 further includes a third step1014 of bringing the object into contact with the polishing zone of thefluid. The method 1000 further includes a fourth step of causing theobject in the polishing zone to move with respect to each other.

Referring now to FIG. 24, yet another embodiment of the presentinvention is shown as method 1100 of polishing an orthopaedic implantarticulating surface. The method 1100 includes a first step 1110 ofcreating a polishing zone within a MP-fluid. The method 1100 furtherincludes a second step 1112 of controlling the consistency of the fluidin the polishing zone. The method 1100 further includes a third step1114 of bringing the object in contact with the polishing zone of thefluids. The method 1100 further includes a fourth step 1116 of causingthe object and the polishing zone to move with respect to each other.The method 1100 further includes a fifth step 1118 of determining therate material removal for the object. The method 1110 further includes asixth step 1120 of determining the direction and velocity of movement ofa polishing zone relative to the object. The method 1100 furtherincludes a seventh step 1122 of determining the number of cycles ofpolishing required.

1. A system for use in preparing an articulating surface of anorthopaedic implant, comprising:a magnetorheological polishing fluidthat includes a carrier fluid and a plurality of particles suspendablein the carrier fluid; a vessel for containing the polishing fluid; amechanism configured to deliver the polishing fluid to form a polishingzone; a holder configured to secure the implant and to moveably positionthe articulating surface of the implant relative to the polishing zone;and a controller configured to (i) determine the rate of materialremoval from the implant, (ii) determine the direction and velocity ofmovement of the polishing zone relative to the implant, and (iii)determine the number of cycles of polishing required, wherein thepolishing fluid comprises magnetic particles having a size of less than100 nm which are coated with silicon carbide.
 2. The system of claim 1,wherein the magnetic particles have a size of less than 50 nm.
 3. Thesystem of claim 1, wherein the plurality of particles comprise at leastone of abrasive particles and magnetic particles.
 4. The system of claim1, wherein the carrier fluid comprises at least one of glycerin, glycol,water, oil, and alcohol.
 5. The system of claim 1, further comprising asurface finish-measuring device operatively connected to the controller,wherein the surface finish-measuring device is configured to provide asignal to the controller indicative of a surface finish of thearticulating surface of the implant.
 6. The system of claim 1, furthercomprising a magnetic field generating device configured to expose thearticulating surface of the implant to a magnetic field so as to altermaterial removing characteristics of the system.
 7. The system of claim1, further comprising a heater configured to elevate temperature of thearticulating surface of the implant so as to alter material removingcharacteristics of the system.
 8. The system of claim 1, furthercomprising a particle-measuring device configured to measure content ofparticles in the magnetorheological-fluid.
 9. The system of claim 8,wherein the particle measuring device is operatively connected to thecontroller to permit the controller to adjust content of particles inthe magnetorheological-fluid so as to optimize material removingcharacteristics of the system.
 10. The system of claim 8, wherein theparticle measuring device is configured to measure electricalconductivity of the magnetorheological polishing fluid.